1. Field of the Invention
The present invention relates to a dynamic damper installed around a rotary shaft, such as a drive shaft of an automobile. The dynamic damper is for suppressing harmful vibrations occurred in the rotary shaft. More particularly, the present invention relates to a dynamic damper which enables to complete the installation thereof around the rotary shaft by fixing one end thereof only to the rotary shaft while maintaining the performances thereof, thereby reducing the manufacturing cost and improving the assembly operability.
2. Related Art Statement
When a rotary shaft, such as a drive shaft and a propeller shaft of an automobile and the like, rotates, unbalanced rotations occur. As a result of the unbalanced rotations, there occurs harmful vibrations like bending vibrations and torsional vibrations. It is naturally preferred that the harmful vibrations should not occur at all. However, various dynamic dampers have been widely used to suppress the harmful vibrations. The dynamic dampers work in the following manner: The dynamic dampers adjust their intrinsic frequencies to the dominant frequencies of the harmful vibrations excited in the rotary shaft, convert the vibration energy of the rotary shaft to the vibration energy of the dynamic dampers by resonance, and absorbs the vibration energy of the rotary shaft.
A conventional dynamic damper whose cross sectional view is illustrated in FIG. 5 has been used for a drive shaft and the like of an automobile. The dynamic damper 600 has a fixing member 601 inserted into and supported by a rotary shaft "S", a cylinder-shaped mass member 602 disposed around the outer periphery of the fixing member 601, and an elastic member 603 disposed between the fixing member 601 and the mass member 602 and connecting the fixing member 601 and the mass member 602.
The intrinsic frequency of this dynamic damper 600 is fundamentally determined by the mass of the mass member 602 and the spring constant of the elastic member 603. The elastic member 603 is subjected to loads in the compression/tensile direction with respect to the vibration of the mass member 602. As a result, the elastic member 603 supports the mass member 602 in the direction exhibiting the compression/tensile spring constant.
The inventor of the present invention proposed a dynamic damper illustrated in FIG. 4 under Japanese patent application No. 213289/1988 which is not laid open at the time of the present application and therefore is not classified as a prior art. The dynamic damper 100 of the earlier application is formed integrally of the following: a pair of fixing members 110, 110 formed in a ring shape; a mass member 120 having an inner surface larger than the outer surface of the rotary shaft "S" and inserted into the rotary shaft "S"; and a pair of elastic members 130, 130 formed in a hollow truncated cone shape and connecting the ends of the fixing members 110, 110 with the ends of the mass member 120. Further, engaging grooves 110a, 110a are formed on the outer surface of the pair of fixing members 110, 110 in a manner going round the outer surface of the fixing members 110, 110, and fixing bands 110b, 110b made of stainless steel and the like are installed around the engaging grooves 110a, 110a, thereby fixing the dynamic damper 100 around the rotary shaft "S". Here, the elastic members 130, 130 support the mass member 120 in the shear direction.
In the above-mentioned conventional dynamic damper 600, the outer diameter thereof tends to increase because the fixing member 601, the elastic member 603 and the mass member 602 are laminated. In addition, when the intrinsic frequency of the dynamic damper 600 should be set in a lower value, the spring constant of the elastic member 603 should be set in a smaller value, or the mass of the mass member 602 should be made greater. However, the shape of the elastic member 603 should be made longer in the vibration direction in order to set the spring constant thereof in a smaller value. This means that the outer diameter of the dynamic damper 600 should be made much greater. Furthermore, the mass of the mass member 602 should be made greater in order to increase the mass of the mass member 602. In this case again, it is inevitable that the outer diameter of the dynamic damper 600 should be made much greater. In this way, it is hard to down-size the conventional dynamic damper 600 while maintaining the performances thereof.
The dynamic damper 100 proposed by the inventor of the present invention under Japanese patent application No. 213289/1988 solves the above-mentioned problems of the conventional dynamic damper 600. To be critical, however, the dynamic damper 100 is slightly poor in the assembly operability because it is installed around the rotary shaft "S" by installing the fixing bands 110b, 110b around the fixing members 110, 110 disposed at the both ends thereof.